// from: http://beej.us/guide/bgnet/html/#getaddrinfoprepare-to-launch

/*
** showip.c -- show IP addresses for a host given on the command line
*/

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>

int main(int argc, char *argv[])
{
    struct addrinfo hints, *res, *p;
    int status;
    char ipstr[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: showip hostname\n");
        return 1;
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // AF_INET or AF_INET6 to force version
    hints.ai_socktype = SOCK_STREAM; // aka TCP.  UDP would be SOCK_DGRAM

    if ((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
        return 2;
    } 

    printf("IP addresses for %s:\n\n", argv[1]);

    for(p = res;p != NULL; p = p->ai_next) {
        void *addr;
        char *ipver;

        // get the pointer to the address itself,
        // different fields in IPv4 and IPv6:
        if (p->ai_family == AF_INET) { // IPv4
            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
            addr = &(ipv4->sin_addr);
            ipver = "IPv4";
	    printf("%x.\n", ((char *)addr)[0]);
        } else if (p->ai_family == AF_INET6) { // IPv6
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
            addr = &(ipv6->sin6_addr);
            ipver = "IPv6";
        } else {
	  printf("What the heck, unknown ai_family 0x%x ...\n", p->ai_family);
	  continue;
	}
	// probably addr is pointing to an address, either IPv4 or IPv6
	for(int k=0; 1; k++) {
	  printf("%hhx.", ((char *)addr)[k]);
	  if (p->ai_family == AF_INET && k == 3) break;
	  else if (p->ai_family == AF_INET6 && k == 15) break;
	}
	printf("\n");

        // convert the IP to a string and print it:
        inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);
	// if inet4, printf("%d.%d.%d.%d\n", addr[0], addr[1], addr[2], addr[3]);
	// if inet6, printf("%02x%02x:%02x%02x:...\n", addr[0], addr[1], ... addr[15]);
        printf("  %s: %s\n", ipver, ipstr);
    }

    freeaddrinfo(res); // free the linked list

    return 0;
}